This bearing is held in place by means of tie rods judiciously disposed in the exhaust endpiece and conveying both normal and accidental forces from the rotor to supporting lugs and to transverse stator centering means, the lugs and the stator transverse centering means bearing against a bed plate.
This constructional disposition allows a degree of weakness to appear. Proper dynamic behavior of the rotor and rotor safety relative to accidental large out-of-balance forces require the bearing to have a high degree of stiffness which is difficult to obtain using a system of tie rods.
In addition, each azimuth corresponds to a different stiffness and this makes it more difficult to support a line of shafts whenever large accidental dynamic out-of-balance forces occur.
All of the forces pass through the bearing or the clamp, the tie rods, the supporting lugs, the stator transverse centering means, and the bed plate.
In addition, the constant increase in the size of exhaust sections is giving rise to dynamic forces of ever increasing magnitude in stators of even bigger sizes.
Document FR-A 75 10810 teaches a gas turbine installation in which the bearing is held by two poles connected to the bed plate.
Such an installation will have poor dynamic behavior since forces are compensated in the vertical direction only, while large forces in the horizontal direction will give rise to major deformation of the structure.
Finally, the poles are long and have insufficient stiffness to withstand large out-of-balance forces.
One of the aims of the support system of the invention is to increase the stiffness of the bearing supporting the rotor and to provide proper support for the bearing against major accidents (e.g. the loss of one of the last low pressure (LP) blades) under the best conditions possible.